This invention relates to door and window systems for use in buildings, particularly but not exclusively in domestic dwellings, and provides a combination sliding and pivoting door or window structure, referred generally hereinafter as a "closure". A principle object of the invention is to provide a closure which combines a sliding panel with a pivoting panel in a manner permitting substantially full and unobstructed access across the width of an opening in which the panels operate, in contrast to conventional sliding closures where, generally, access is only available to half of the width of an opening containing a pair of closure panels.